The de novo design of folded polypeptides aims at improving our understanding of protein structure, and also provides a platform for the engineering of new proteins with tailored functions [DeGrado, W. F.; Summa, C. M.; Pavone, V.; Nastri, F.; Lombardi, A. Annu. Rev. Biochem. 1999, 68, 779-819; Micklatcher, C.; Chmielewski, J. Curr. Opin. Chem. Biol. 1999, 3, 724-729; Baltzer, L.; Nilsson, H.; Nilsson, J. Chem. Rev, 101, 3153-3164. Designed, folded polypeptides that undergo pH-controlled, site selective self-functionalization with ligands [Broo, K.; Brive, L.; Lundh, A. C.; Ahlberg, P.; Baltzer, L. J. Am. Chem. Soc. 1996, 118, 8172-8173; Baltzer, L.; Nilsson, J. Curr. Opin. Biotechnol. 2001, 12, 355-360] constitute an excellent toolbox for the construction of various complex molecular systems, e. g. model glycoproteins [Andersson, L.; Stenhagen, G.; Baltzer, L. J. Org. Chem. 1998, 63, 1366-1367; Andersson, L. K.; Dolphin, G. T.; Kihlberg, J.; Baltzer, L. J. Chem. Soc.-Perkin Trans. 2 2000, 459-464] or complex receptors.